1. Field of the Invention
This invention relates to a preservative auxiliary material for foods, etc., comprising white sweet potato (Simon). More particularly, it relates to an auxiliary material applicable to the whole range of foods as well as to animal feeds which can substantially improve the keeping qualities of a product when used together with a main material.
2. Description of the Prior Art
Foods are denatured in various manners since the production thereof till the intake thereof by consumers. There are a number of factors causing such denaturation, for example, microorganisms, oxidation with oxygen, autolysis with enzymes, biological actions, chemical reactions among ingredients, dissipation of ingredients and physicochemical changes of ingredients. The denaturation is caused not by a single factor, from among the above-mentioned ones, but by two or more factors tangled together. In the preservation of foods, putrefaction caused by microorganisms (i.e., "molds") and deterioration due to oxidation generally bring about the most serious problems.
It is difficult, in the case of some foods, to provide a effective means for preventing the putrefaction. Thus the deterioration caused by molds can be prevented in only limited cases wherein treatments including canning, freezing, drying and heating are available.
Regarding the deterioration due to oxidation, it is hard to state that there have been established techniques which are effective in practice. This is because the permeation of a gas such as oxygen in the form of molecules can be hardly inhibited, even once removed, as compared with microorganisms the invasion of which can be completely prevented.
The deterioration due to oxidation, which is a serious problem in foods, is caused by the oxidation of lipids contained in foods. Foods, in particular, vegetable foods generally contain little lipids. However the lipids contained in vegetable foods comprise unsaturated fatty acids which are liable to undergo oxidation and, as a result, rancidification. When the chain oxidation proceeds, furthermore, ingredients such as ascorbic acid, colorants and odor components are denatured and rancidified, thus bringing about various disadvantages. When a food is oxidized, therefore, several problems including the evolution of an offensive odor, an increase in viscosity and a color change will be observed.
In order to prevent the growth of molds or the oxidation of lipids, there have been widely employed microbicides or preservatives and antioxidants. However most of these agents are organic compounds which are not harmless to human body. Thus it has been pointed out that they might cause internal organ diseases and exert other adverse effects on the human body. In particular, some of these compounds are carcinogenic or teratogenic and thus tolerances therefor have been specified. However the continuous use of such agents might have bad influences (for example, residence in the human body), even though they are used in an amount below the tolerant level. Accordingly it is desirable not only for man but also for livestock to avoid unnecessary intake of these agents.
The white sweet potato (Simon) to be used as the starting material in the present invention is the foundation stock of potatoes. It was once used as a nostrum by Amerinds in Central and South America. Later this plant was improved and then named Simon after the discoverer thereof. It was introduced into Japan recently and cultivated. It has been confirmed so far that Simon contains vitamins A, B.sub.1, B.sub.2, B.sub.6, C, E, P and K, nicotinic acid, pantothenic acid, porphyrin, folic acid, chlorophyll, calcium, potassium, iron, magnesium, etc. Although it is highly nutritious, it is inferior to common sweet potato in starch content and sugar content. Thus it has not been fully utilized but rather allowed to stand hitherto.
However the present inventor's efforts have made the white sweet potato available as a material of sake (refer to Japanese Patent No. 1516489). The white sweet potato can be grown not only in fields but also in non-cultivated paddy fields by extensive cultivation. Further, it is highly fertile and shows an elevated yield potential, since not only the tuberous root but also the foliage can be utilized. Thus there is a good possibility that the white sweet potato can substitute for rice. Furthermore, the exploitation of the usefulness of the white sweet potato which is highly nutritious may be useful for farmers.